1. Technical Field
The present invention relates to a power assist steering system. In particular, the present invention relates to an electric power assist steering system which includes a ball nut for transmitting force between a steering member and an electric assist motor.
2. Description of the Prior
A known type of power assist steering system includes a ball nut for transmitting force between a steering member and an electric assist motor. Upon actuation of the electric motor, the ball nut is driven to rotate relative to the steering member. The rotational force of the ball nut is transmitted to the steering member to drive the steering member axially. Axial movement of the steering member effects turning movement of the steerable wheels of the vehicle.
In some known electric power assist steering systems, the ball nut is located inside the motor, that is, radially within the rotor and the stator. This arrangement tends to decrease the size of the rotor, thus reducing motor efficiency, unless the radial size of the motor is increased. In other known steering systems, the ball nut is located axially outside the motor. This arrangement tends to increase the length of the steering assembly, again undesirably.